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Fault Slip Model for the 12 May 2008 Wenchuan-Beichuan Mw 7.9 earthquake in Sichuan, China from ALOS, Envisat and other satellite data

Eric Fielding(1), Roland Bürgmann(2), Gareth Funning(3), Zhenhong Li(4) and Isabelle Ryder(2)

(1) Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Drive, Pasadena, California 91109, United States
(2) University of California, Berkeley, McCone Hall, Berkeley, California, United States
(3) University of California, Riverside, Geology Building, rm 2326, Riverside, CA 92521, United States
(4) COMET*, University of Glasgow, East Quadrangle, Glasgow G12 8QQ, United Kingdom

Abstract

A Mw 7.9 earthquake struck Sichuan province on 12 May 2008 causing catastrophic damage over a large area including the county seats of Wenchuan and Beichuan. Preliminary seismic modelling indicates a fault rupture roughly 250 km long with a strike of 229° (C. Ji and G. Hayes, http://earthquake.usgs.gov/eqcenter/eqinthenews/2008/us2008ryan/finite_fault.php) in the Longmenshan mountains at the steep eastern edge of the Tibetan Plateau. At the time of this writing (1 June 2008), ALOS PALSAR coseismic pairs have been processed for two ascending paths over the area. Path 473 crosses the earthquake rupture at 104.5° E and includes Beichuan and Mianyang. Interferograms and SAR pixels offset measurements using the 19 May scene from this path show a surface rupture with up to 4 m of slip on a fault or faults close to what has been called the Beichuan fault (Densmore et al., Tectonics, 2007) that passes close to the devastated Beichuan. Path 476 covers the southwest end of the earthquake, approximately 150 km to the west. A coseismic interferogram and SAR pixel offsets using the 24 May scene show no clear surface rupture but reflect slip at depth on an extension of the fault to the southwest of the epicenter. Along-track coseismic pixel offsets for both paths 473 and 476 have large amplitude ripples or waves that are likely due to ionospheric disturbances. Coseismic pairs for paths 470 to 472, 474, 475, and 477 should eventually cover the entire earthquake deformation. Several post-quake descending PALSAR scenes have been acquired in ScanSAR mode, but it is not yet clear whether there will be any burst alignment with pre-quake scenes to allow InSAR processing. Envisat ASAR has acquired a number of scenes of Sichuan after the earthquake in high-resolution strip-map modes with a variety of image beams and VV polarization. Unfortunately, out of the first seven scenes acquired, only the descending track 18 acquisition on 28 May has a mode and polarization consistent with previous acquisitions that could allow InSAR analysis. The first ScanSAR ASAR acquisitions (wide-swath, WS mode), HH polarization, are planned for 10 and 13 June, and these tracks 204 and 247 have a number of pre-quake acquisitions since the great improvement of the WS burst alignment in late 2006. If the InSAR coherence at C-band wavelength is good for WS-WS interferograms in Sichuan these should cover the entire fault. Acknowledgements: Part of this research was performed at the Jet Propulsion Laboratory, Caltech under contract with NASA. ALOS PALSAR and ENVISAT ASAR data were provided through JAXA ALOS AO project (ID: P0610001, PI: I. Dowman; AADN ID: 136, PI: E. Fielding; AADN ID: 168, PI: R. Bürgmann), ASF AADN UPASS project (ASF ID 90, PI: I. Ryder), ESA AOE-668 (PI: E. Fielding) and DRAGON 2558 (PI: Q. Zeng). *COMET: Centre for the Observation and Modelling of Earthquakes and Tectonics #: Co-authors are in alphabetical order

 

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